Endocrine 2

• Endocrine System


  System that produces hormones, chemical messengers that regulate various bodily processes

  
• Lecture Outline


  • Classification of Hormones
  • Mechanism of Hormonal Action
  • Endocrine Glands, Hormones, and Functions
  • Endocrine Disorders
• Hormones


  Chemical messengers secreted by endocrine glands that regulate various bodily processes

  
• Glands


  Organs that secrete hormones
• Endocrinology


  Study of the endocrine system and its functions

  
• Chemical messengers


  Substances that convey signals from one part of the body to another
• Mechanism of Hormonal Action

  1. Opening or closing channels

  2. Activating second-messenger systems

  3. Activated by first messenger

  4. Relays message to intracellular proteins that carry out dictated response

  
• Types of Chemical Messengers

  • Neurotransmitters and neuropeptides
  • Paracrines
  • Hormones
  • Neurohormones
• Neurotransmitters and neuropeptides


  Short-range chemical messengers that diffuse across narrow space to act locally on adjoining target cell
• Paracrines


  Local chemical messengers that exert effect only on neighboring cells in immediate environment of secretion site
• Hormones


  Long-range messengers secreted into blood by endocrine glands in response to appropriate signal, exerting effect on target cells some distance away from release site

  
• Neurohormones


  Hormones released into blood by neurosecretory neurons, distributed through blood to distant target cells

  
• Classification of Hormones


  • Hydrophilic hormones (proteins, peptides)
  • Lipophilic hormones (steroids)

  
• Hydrophilic hormones


  Highly water soluble, low lipid solubility
• Lipophilic hormones


  High lipid solubility, poorly soluble in water
• Peptide Hormone Synthesis


  1. Preprohormones

  2. Prohormones

  3. Active hormones

  4. Storage

  5. Exocytosis
• Steroid Hormones Synthesis


  1. Cholesterol modification

  2. No storage

  3. Release via diffusion

  
• Amine Hormones Synthesis


  1. Tyrosine precursor

  2. Storage (thyroid hormones in thyroglobulin, catecholamines in secretory vessels)

  3. Secretion (thyroid hormones, dopamine, norepinephrine, epinephrine)

  
• Hormonal Transport


  Hydrophilic hormones dissolved in plasma, bound to specific carrier proteins

  Lipophilic steroids and thyroid hormones bound to plasma proteins (albumin)

  Catecholamines 50% circulate as free hormones, 50% loosely bound to albumin

  
• Mechanisms of Hormone Action

  • Membrane receptors (hydrophilic peptides and catecholamines)
  • Internal receptors (lipophilic steroids and thyroid hormones)

  
• Membrane receptor mechanism


  Alter conformation of adjacent ion channels, activate second-messenger system

  
• Internal receptor mechanism


  Hormone response element (HRE)
• Factors Affecting Effective Plasma Hormone Concentration

  • Hormone's rate of secretion into the blood
  • Rates of metabolic activation (for a few hormones)
  • Extent of binding to plasma proteins (for lipophilic hormones)
  • Rate of removal from the circulation
  • Responsiveness of target cell receptors

  
• Hormone Regulation


  Effective plasma concentration normally regulated by changes in hormone's rate of secretion

  
• Hormone-Hormone Interactions


  • Permissiveness
  • Synergism
  • Antagonism
• Permissiveness


  One hormone is present in adequate amounts for full exertion of another hormone's effect
• Synergism


  Complementary effects of several hormones
• Antagonism


  One hormone causes the loss of another hormone's receptors
• Mechanisms of Hormone Regulation

  • Negative-feedback Control
  • Neuroendocrine Reflexes
  • Circadian and Other Biological Rhythms

  
• A single hormone may be secreted by several endocrine glands
• A single endocrine gland may secrete several hormones
• A single hormone has more than one type of target cell and therefore can induce more than one type of effect
• The secretion rate of some hormones varies considerably over the course of time in a cyclic pattern
• A single target cell may be influenced by more than one hormone
• The same chemical messenger may be either a hormone or a neurotransmitter, depending on its source and mode of delivery to the target cell
• Some organs are exclusively endocrine in function, whereas other organs of the endocrine system perform nonendocrine functions
• Endocrine Disrupting Chemicals


  Chemicals that interfere with the endocrine system, found in household products, affecting sexual development of vertebrate brains

  
• In nonvertebrates, hormones are produced by neuroendocrine cells or distinct glands in neural hemal organs

  
• Endocrine Disorders


  • Hyposecretion
  • Hypersecretion
  • Decreased responsiveness of target cells
• Pineal Gland


  Located in the center of the brain, produces melatonin to regulate circadian rhythm, receives input from suprachiasmatic nucleus and melanopsin-containing retinal cells